Taeniid cestode infections in man and animals constitute a serious zoonotic and economic problem throughout the world. Fundamental to the continuity of the life cycles of these parasites is the ability of the larval stages to survive for extended periods of time within the tissues of mammalian intermediate hosts. That they are able to do so in immunologically competent animals, which may show a marked and specific antibody-mediated immunity to superinfection, is a paradox challenging to our understanding of resistance mechanisms in infectious disease. Existing hypotheses seek to account for this failure of immunological rejection in terms of isolation of parasites by tissue reactions, molecular mimicry (production of host-like antigens by the parasite) or masking of parasite antigenic determinants by the adsorption of host components. The purpose of this project is to examine immunological events during taeniid metacestode infection. Particular emphasis will be placed on interactions between parasite membranes, antibody, complement and both specific and nonspecific effector cells. Ultrastructural, pathological, and immunochemical techniques will be used to explore the mechanisms involved in immunologic attack on the parasite, and the means whereby established parasites are able to retain control of membrane function and preserve membrane integrity in the face of immunologic reactions on the part of the host. Growth and development in normal and immune hosts will be studied in an effort to determine the factors which characterize host cell reactivity in infected tissues. The immunogenicity of well defined parasite products will be studied. BIBLIOGRAPHIC REFERENCES: Musoke, A.J., and J.F. Williams. 1976. The immunological response of the rate to infection with Taenia taeniaeformis. III. Antibody response to implanted parasites. Int. J. Parasitol. (In Press). Ansari, A., and J.F. Williams. 1976. The eosinophilic response of the rat to infection with Taenia taeniaeformis. J. Parasitol. (In Press).